1. Field
The present disclosure generally relates to techniques for designing and manufacturing integrated circuits (ICs). More specifically, the present disclosure relates to a method and an apparatus for modifying input/output (referred to as “I/O” hereafter) cell placement in an IC die when die size changes.
2. Related Art
Dramatic improvements in semiconductor integration circuit (IC) technology presently make it possible to integrate hundreds of millions of transistors onto a single semiconductor IC chip. These improvements in integration densities have largely been achieved through corresponding improvements in semiconductor manufacturing technologies, which have recently achieved ultra-deep-submicron feature sizes. On the flip side, the constant drive toward ever-decreasing feature sizes has led to a significant increase in IC manufacturing costs.
One way to alleviate the increasing IC fabrication cost is to achieve design specifications using a minimum feasible die size. For example, some chip floor planning tools can automatically analyze IC design constraints and identify the smallest routable die size for tape-out. Alternatively, a designer can explore the minimum feasible die size manually.
While exploring the minimum feasible die size of an IC design, the designers need a tool to refit all the original I/O pads and other I/O cells into different shrunk or expanded die boundaries while maintaining the original side, relative order, and alignment of the I/O cells. Conventionally, this is achieved by performing a new cell-by-cell-based placement process from the original I/O placement under certain design constraints. However, this “re-placement” technique has a number of limitations, such as the original design constraints not being appropriate for a changed die size, inability to handle macro cells inside the I/O area, inability to handle multiple I/O rings, and inability to handle rectilinear shaped I/O cells.
Hence, what is a needed is an I/O cell re-placement technique during die-size optimization without above-described problems.